1. Field of the Invention
The present invention relates to a method and apparatus for creating a flap in a live cornea of an eye and creating incisions or shrinkage under the flap, as appropriate, to correct vision disorders without damaging the Bowman""s layer of the eye. More particularly, the present invention relates to an apparatus and method employing a cutting tool, such as a blade, water jet or laser, that can be directed to cut a flap in a live cornea, along with incisions or shrinkage under the flap, as appropriate, to correct vision disorders such as astigmatism, myopia, hyperopia or presbyopia, when the flap is allowed to relax back onto the remainder of the cornea and the incisions and shrinkage areas are permitted to heal.
2. Description of the Related Art
A normal ametropic eye includes a cornea, lens and retina. The cornea and lens of a normal eye cooperatively focus light entering the eye from a far point, i.e., infinity, onto the retina. However, an eye can have a disorder known as ametropia, which is the inability of the lens and cornea to focus the far point correctly on the retina. Typical types of ametropia are myopia, hypertrophic or hyperopia, astigmatism and presbyopia.
A myopic eye has either an axial length that is longer than that of a normal ametropic eye, or a cornea or lens having a refractive power stronger than that of the cornea and lens of an ametropic eye. This stronger refractive power causes the far point to be projected in front of the retina.
Conversely, a hypermetropic or hyperopic eye has an axial lens shorter than that of a normal ametropic eye, or a lens or cornea having a refractive power less than that of a lens and cornea of an ametropic eye. This lesser refractive power causes the far point to be focused on the back of the retina.
An eye suffering from astigmatism has a defect in the lens or shape of the cornea. Therefore, an astigmatic eye is incapable of sharply focusing images on the retina.
In order to compensate for the above deficiencies, optical methods have been developed which involve the placement of lenses in front of the eye (for example, in the form of glasses or contact lenses). However, this technique is often ineffective in correcting severe vision disorders.
An alternative technique is surgery. For example, in a technique known as myopic keratomileucis, a microkeratome is used to cut away a portion of the front of the live cornea from the main section of the live cornea. That cut portion of the cornea is then frozen and placed in a cyrolathe where it is cut and reshaped. Altering the shape of the cut portion of the cornea changes the refractive power of this cut portion, which thus effects the location at which light entering the cut portion of the cornea is focused. The reshaped cut portion of the cornea is then reattached to the main portion of the live cornea. Hence, this reshaped cornea will change the position at which the light entering the eye through the cut portion is focused, so that the light is focused more precisely on the retina, thus remedying the ametropic condition.
Keratophakia is another known surgical technique for correcting severe ametropic conditions of the eye by altering the shape of the eye""s cornea. In this technique, an artificial organic or synthetic lens is implanted inside the cornea to thereby alter the shape of the cornea and thus change its refractive power. Accordingly, as with the myopic keratomileucis technique, it is desirable that the shape of the cornea be altered to a degree which enables light entering the eye to be focused correctly on the retina.
A further known surgical technique is radial keratotomy. This technique involves cutting numerous slits in the front surface of the cornea to alter the shape of the cornea and thus, alter the refractive power of the cornea. It is desirable that the altered shape of the cornea enables light entering the eye to be focused correctly on the retina. However, this technique generally causes severe damage to the Bowman""s layer of the cornea, which results in scarring. This damage and scarring results in glare that is experienced by the patient, and also creates a general instability of the cornea. Accordingly, this technique has generally been abandoned by most practitioners.
Laser in situ keratomileusis (LASIK), as described, for example, in U.S. Pat. No. 4,840,175 to Peyman, the entire contents of which is incorporated herein by reference, is a further known surgical technique for correcting severe ametropic conditions of the eye by altering the shape of the eye""s cornea. In the LASIK technique, a motorized blade is used to separate a thin layer of the front of the cornea from the remainder of the cornea in the form of a flap. The flap portion of the cornea is lifted to expose an inner surface of the cornea. The exposed inner surface of the cornea is irradiated with laser light, ablated and thus reshaped by the laser light. The flap portion of the cornea is then repositioned over the reshaped portion and allowed to heal.
In the LASIK technique, it is critical that the tissue ablation is made with an excimer laser, which is difficult to operate and is very expensive. In addition. the process requires tissue removal which might lead to thinning of the cornea or ectasia, which is abnormal bulging of the cornea that can adversely affect vision.
In all of the above techniques, it is necessary that the cornea be prevented from moving while the cutting or separating of the corneal layers is being performed. Also, it is necessary to flatten out the front portion of the cornea when the corneal layers are being separated or cut so that the separation or cut between the layers can be made at a uniform distance from the front surface of the cornea. Previous techniques for flatting out the front surface of the cornea involve applying pressure to the front surface of the cornea with an instrument such as a flat plate.
In addition to stabilizing the cornea when the cutting or separating is being performed, the cutting tool must be accurately guided to the exact area at which the cornea is to be cut. Also, the cutting tool must be capable of separating layers of the cornea without damaging those layers or the surrounding layers.
Furthermore, when the keratotomy technique is being performed, it is desirable to separate the front layer from the live cornea so that the front layer becomes a flap-like layer that is pivotally attached to the remainder of the cornea and which can be pivoted to expose an interior layer of the live cornea on which the implant can be positioned or which can be ablated by the laser. However, these methods disturb the optical axis of the eye, which passes through the center of the front-portion of the cornea and extends longitudinally through the eye. Care also must be taken so as not to damage the Bowman""s layer of the eye.
In addition, because the epithelium cells which are present on the surface of the live cornea may become attached to the blade when the blade is being inserted into the live cornea and thus become lodged between the layers of the live cornea, thereby clouding the vision of the eye, it is desirable to remove the epithelium cells prior to performing the cutting.
Examples of known apparatuses for cutting incisions in the cornea and modifying the shape of the cornea are described in U.S. Pat. No. 5,964,776 to Peyman, U.S. Pat. No. 5,919,185 to Peyman, U.S. Pat. No. 5,722,971 to Peyman, U.S. Pat. No. 4,298,004 to Schachar et al., U.S. Pat. No. 5,215,104 to Steinert, and U.S. Pat. No. 4,903,695 to Warner.
A need exists for an improved apparatus and method for cutting a flap and, if appropriate, one or more incisions in a live cornea to correct vision disorders. Specifically, a need exists for an improved apparatus and method which corrects vision disorders without ablating or removing tissue from the cornea, without placing an insert in the cornea and, most importantly, without damaging the Bowman""s layer.
An object of the present invention is to provide an apparatus and method for precisely forming a flap in a live cornea and then, if desired, forming incisions and tissue shrinkage in the live cornea under the flap without ablating or removing tissue from the cornea, or implanting any material in the cornea, to correct vision disorders in the eye.
Another object of the present invention is to provide an apparatus and method for precisely forming a flap in a live cornea without disturbing the optical axis or Bowman""s layer of the eye.
A further object of the present invention is to provide an apparatus and method for precisely forming a flap in the live cornea about at least a portion of the circumference of the live cornea, and then, if desired, forming incisions or tissue shrinkage in the live cornea under the flap without removing or ablating any tissue, to correct vision disorders in the eye such as astigmatism, myopia, hypertrophic, hyperopia and presbyopia, to name a few.
This and other objects of the present invention are substantially achieved by an apparatus and method for forming a flap in a live cornea of any eye to correct vision disorders in the eye such as astigmatism, myopia, hypertrophic, hyperopia and presbyopia. The apparatus and method employ a stabilizing device and a cutting tool. The stabilizing device is adapted to be attached to the front surface of a live cornea to apply suction to the live cornea which prevents the live cornea from moving when the cutting is being performed. The stabilizing device includes a transparent or substantially transparent viewer through which the front surface of the cornea to which the suction is being applied can be viewed. The suction pulls the front surface of the cornea in a direction toward the viewer so that the front surface of the cornea contacts a bottom surface of the viewer and thus flattens out against that bottom surface. The cutting tool can be, for example, a blade, water jet, laser, or any combination thereof, that is directed toward the cornea that is stabilized in the stabilizing device to cut the flap in the cornea, which can be through the front surface of the cornea about at least a portion of the periphery of the cornea, or can be through the front surface of the cornea is a manner similar to the LASIK procedure described above. Any of the cutting tools can further be used to cut differently-shaped incisions under the flap, such as radial incisions, actuate incisions, and so on, as desired, to correct the vision disorder. Tools such as a laser, diathermy device, or microwave emitting device can be used, as desired, to create shrinkage under the flap without ablating the tissue or removing any tissue, to further correct vision disorders.